If you don't want to get the full single-speed conversion for the tranny, I would definitely get the steel idler as mentioned and also the gear coupler (the do-hicky in the lower right corner):
This will lock it in second gear better than trying to rig the dog gear so it's locked. Also gets rid of the slop from the dog gear.
I don't think Mike has this part listed, but he can get it for you...